Topological modes in a laser cavity through exceptional state transfer.

Shaping the light emission characteristics of laser systems is of great importance in various areas of science and technology. In a typical lasing arrangement, the transverse spatial profile of a laser mode tends to remain self-similar throughout the entire cavity. Going beyond this paradigm, we demonstrate here how to shape a spatially evolving mode such that it faithfully settles into a pair of bi-orthogonal states at the two opposing facets of a laser cavity. This was achieved by purposely designing a structure that allows the lasing mode to encircle a non-Hermitian exceptional point while deliberately avoiding non-adiabatic jumps. The resulting state transfer reflects the unique topology of the associated Riemann surfaces associated with this singularity. Our approach provides a route to developing versatile mode-selective active devices and sheds light on the interesting topological features of exceptional points.

Ultrasensitive micro-scale parity-time-symmetric ring laser gyroscope.

We propose a new scheme for ultrasensitive laser gyroscopes that utilizes the physics of exceptional points. By exploiting the properties of such non-Hermitian degeneracies, we show that the rotation-induced frequency splitting becomes proportional to the square root of the gyration speed (Ω), thus enhancing the sensitivity to low angular rotations by orders of magnitudes. In addition, at its maximum sensitivity limit, the measurable spectral splitting is independent of the radius of the rings involved. This Letter paves the way toward a new class of ultrasensitive miniature ring laser gyroscopes on chip.

Dark-state lasers: mode management using exceptional points.

By exploiting the inherent characteristics of dark-state resonators, we experimentally realize a single-frequency integrated microring laser system. This semiconductor laser can remain single-mode, even at high pump power levels, while allowing tunability over a wide spectral range. Our results demonstrate the potential of exceptional points as a versatile tool for mode selection in micro-cavity laser configurations.

Parity-time-symmetric coupled microring lasers operating around an exceptional point.

The behavior of a parity-time-symmetric coupled microring system is studied when operating in the vicinity of an exceptional point. Using the abrupt phase transition around this point, stable single-mode lasing is demonstrated in spectrally multimoded microring arrangements.